Tomographic PIV Experimental Study on Motion of Rising Single Bubble

In order to uncover the wake vortex structures and their interaction with the bubble, the shadow image method and the tomographic PIV were used respectively to conduct experiments on the process of a single bubble with a zigzag path rising freely in quiescent water. Therefore, the bubble shape, motion and three-dimensional wake velocity field were obtained. Using the λci vortex criterion and the finite-time Lyapunov exponent (FTLE), the three-dimensional wake vortex structures and the two-dimensional Lagrangian coherent structures(LCS) were identified from the velocity field. The results show that during the zigzag rising process, there is a vortex ring around the bubble, and oppositely-oriented hairpin vortices shed alternately from the vortex ring along the bubble path. During the shedding of a single hairpin vortex, the FTLE ridges at the bottom of the bubble will form an asymmetrical flux window. The conclusions can be drawn from these results. First, the periodic shedding of the hairpin vortices periodically and alternately breaks the symmetry of the vortex ring relative to the bubble, resulting in the periodic zigzag motion of the bubble. Second, during the shedding of a single hairpin vortex, the fluid transport from one side of the vortex ring to the hairpin vortex is different from the other side's. © 2022, Editorial Department of Journal of Propulsion Technology. All right reserved.